Mitochondrial degeneration and dysfunction are a hallmark of aging and aging-related human diseases, including Alzheimer disease, Parkinson disease, Huntington disease, cancer, type 2 diabetes, atherosclerosis, and cardiovascular diseases. Consequently, mitochondria have evolved several surveillance strategies to protect the organelle from damage. At the same time, factors that target mitochondrial proteins and selectively induce apoptosis, for instance of cancer cells, are actively sought after. The mitochondria provide a paradigm to elucidate the network of molecular chaperones and energy-dependent proteases, which function synergistically to maintain protein homeostasis in the mitochondrial matrix. It is widely appreciated that molecular chaperones provide the first line of defense against protein misfolding diseases by promoting folding and preventing aberrant folding and protein aggregation. In addition to their role in protein folding, mitochondrial chaperones, such as Mortalin (mtHsp70) and TRAP1 (mtHsp90) are also widely expressed in most tumor cell types, including colorectal, breast, prostate, and ovarian cancer, which have the highest mortality rates, but strikingly not in highly proliferating, non-tumor cells. Remarkably, down- regulation of TRAP1 abrogates the transforming potential of osteosarcoma, colon carcinoma, and cervix carcinoma cells, supporting a new role of mitochondrial chaperones in the immortalization of cancer cells. Consistently, inhibition of TRAP1 induces apoptosis in prostate cancer cells, underscoring the significance of mitochondrial chaperones as promising new drug targets. The broad and long-term research objective is to provide a molecular understanding of the mitochondrial protein quality control system in vitro and in vivo, to determine the underlying cooperative mechanism and function of the mitochondrial protein folding machinery in normal and pathological states, and how small molecules can be used to modulate mitochondrial chaperone function. The goals of this research will be pursued through the following specific aims: 1) to characterize the mitochondrial protein folding machinery in normal and disease states; 2) to target the structure of TRAP1 with small molecule compounds to modulate its chaperone function; and 3) to determine the structural and molecular basis of TRAP1-substrate interaction. To accomplish our research objective, we will use a multi-pronged in vitro and in vivo approach, which spans different resolution scales and adds to the innovation of the proposed research.